1. Field of the Invention
The present invention relates to wafer processing systems, and in particular, to a manifold for reducing unwanted particles generated in a cool chamber.
2. Description of the Prior Art
Semiconductor wafer processing is a complex procedure performed by large semiconductor wafer processing systems that include many chambers where the semiconductor wafers are processed.
Wafer processing systems employ cool chambers for cooling wafers that have been heated to high temperatures in other processing chambers. For example, in physical vapor deposition (PVD) chambers, wafers are exposed to plasma and heaters that can heat the wafers to high temperatures, such as temperatures in the 200 to 300 degrees Celsius range. Thereafter, the wafers must be cooled before removing the wafers from the system. Cool chambers are provided for this purpose.
FIG. 1 illustrates a conventional cool chamber 2 that employs a single inlet port 4 that allows a cooling gas to flow into the chamber 2 and onto a wafer 7. Cool chambers 2 operate on the principle that when the pressure of the chamber 2 is elevated by filling the chamber 2 with a gas, the gas molecules provide a conduction medium to pull heat away from the wafer 7 and transfer the heat to the gas molecules. An inert gas, such as Argon, can be used to fill the cool chamber 2. The chamber 2 includes a wafer pedestal 6 that supports the wafer 7. It should be noted that the inlet port 4 is at a height that is approximately at the height of the top surface of the wafer pedestal 6. Accordingly, the gas is directed at about the same horizontal plane in which the wafer 7 is disposed. For example, the gas can be regulated to enter the cool chamber at a rate of 200 mTorr/sec for 10 seconds. After an additional 30 seconds (i.e., the approximate time needed for the wafer 7 to cool to a sufficiently low temperature), the wafer 7 is removed from the cool chamber 2.
Unfortunately, conventional cool chambers suffer from several drawbacks. First, since the gas is directed to flow, in a concentrated manner, from a single inlet 4 towards the wafer 7 in the plane of the wafer 7, the high velocity gas particles have a propensity to dislodge or stir up unwanted particles from the wafer 7 or the wafer pedestal 6. These unwanted particles can contaminate the wafer 7 and adversely affect the final product (e.g., the integrated circuit). In fact, a high particle level in any process chamber is known to adversely affect manufacturing yields. For example, the bottom surface of the wafer 7 may have accumulated particles from the other process chambers that may now be dislodged by the gas. Moreover, the wafer pedestal 6 itself can have residue particles from a previous wafer or other source, which also can be dislodged by the gas.
Second, the gas tends to cause the wafer 7 to slide on the pedestal 6. Unfortunately, any movement, even slight movement, can cause particle generation by the abrasive rubbing of the wafer 7 against the pedestal 6. For example, particles can be generated by the pedestal surface rubbing against the film deposited on the bottom surface of the wafer 7.
To address these problems, attempts were made to reduce the inlet gas flow. However, by reducing the inlet gas flow, the processing time to cool a wafer is increased significantly. In addition, since all wafers must go through the cool chamber, the increased processing time to cool the wafer increases the processing time for all wafers that proceed through the wafer processing system.
An alternative approach to this problem is to employ fingers to hold the wafer 7 in place on the pedestal 6 to reduce the likelihood of movement of the wafer 7. Unfortunately, this approach suffers from the following drawbacks. First, the fingers used to hold the wafer 7 can also dislodge particles from the top surface of the wafer 7. Second, although this approach reduces the likelihood of movement of the wafer 7, it does not eliminate the possibility of such movement. Third, this approach does not adequately address the situation where the gas flowing towards the wafer 7 can dislodge particles and increase the number of unwanted particles in the chamber 2 which, as explained previously, reduces manufacturing yields in processing.
Accordingly, there remains a need for a method and apparatus for reducing the generation of unwanted particles in a cool chamber that overcomes the problems set forth above.